In an electrophotographic process used in a laser beam printer, a fax machine and so forth, various durability properties are desired since an electrophotographic photoreceptor undergoes the action of electrification, exposure to light, development, transfer, cleaning, removal of electrification and so forth. Specifically, mechanical strength such as wear resistance and scratch resistance is to be a large factor to determine the durability life.
In the electrophotographic process, cleaning is largely associated with the mechanical strength such as wear resistance of the photoreceptor. In recent years, with small-sizing of developer particles, higher precision cleaning has been demanded. Further, in line with small-footprinting of an apparatus, application of blade cleaning has an advantage in realization of a simpler apparatus structure. The blade cleaning is composed of a simple structure in which an elastic member formed from plate-shaped polyurethane or such is simply thrust in the bus bar direction of the photoreceptor. However, in this case, wear of the photoreceptor is accelerated, whereby a decline of durability is generated. In order to deal with the foregoing subject, it is effective to reduce frictional force with the blade by providing lubricity to the photoreceptor or to provide strength durable against frictional force with the photoreceptor.
First, in order to provide lubricity to the photoreceptor, addition of a material having low surface energy is effective, but addition of a fluorine resin is more effective (refer to Patent Documents 1 and 2, for example). Polytetrafluoroethylene (PTFE) possesses the lowest surface energy and exhibits excellent lubricity and nonadhesiveness among fluorine resins, and also a conventional PTFE containing no fluorine at the terminal exhibits lubricity and nonadhesiveness together with water and oil repellency immediately after coating and film formation, but the water and oil repellency tends to be lowered, resulting in an insufficient practical application in a present situation. Further, in the case of excessive addition of PTFE into a coating solution to maintain high oil repellency, a mechanical strength of a film becomes insufficient since PTFE itself is very flexible, resulting deterioration of filming and scratch resistance.
Next, in order to provide strength durable against frictional force to the photoreceptor, it is effective to produce a high molecular binder resin or to use a curable binder resin. However, in a coating process as a major manufacturing process of an organic photoreceptor, production of high molecular binder resins is to be limited since the high molecular binder resin causes thickening of a coating material. In the case of conventional curable binder resins, an insufficient photoconductive property tends to be obtained since reaction of an organic photoconductive material is deteriorated during curing, and an impurity level is formed by an unreacted functional group, a polymerization initiator by-product.
For example, a surface layer exhibiting mechanical strength is possible to be obtained via radical polymerization of monomers or oligomers having an acrylate group or a methacrylate group as a most readily curable material (refer to Patent Document 3, for example). These have a carboxylic acid ester structure having an acrylate group or a methacrylate group, and exhibit high moisture adsorption. Further, there is a drawback such that a curable material exhibits insufficient moisture resistance, since an initiator to start radical polymerization tends to form a moisture adsorption decomposed product via decomposition of the initiator. The decomposed product of the initiator tends also to act as a trap of photocarriers, causing another drawback in which photoreceptor characteristics are deteriorated. Further, there is a problem such that a curing process is not sufficiently accelerated in the case of a film as utilized for a photoreceptor, since radical polymerization is inhibited by oxygen in the air.
On the other hand, typical cationic polymerizing compounds are vinyl ether compounds or epoxy compounds (Patent Documents 4 and 5, for example), but a longer curing time is consumed since polymerization reaction is difficult to be accelerated in comparison to radical polymerization, whereby desired mechanical strength can not be obtained. Further, there is another problem such that in the case of a photoreceptor in which particles are added into a cationic polymerizing compound, particles settle out via aging when a compound to start cationic polymerization used for reaction-curing a cationic polymerizing compound is added into a dispersion, and particles are coagulated during coating a surface layer, whereby smoothness and transparency of a coated layer is to be deteriorated.
When a conventional PTFE containing no fluorine at the terminal is also employed as a compound to start cationic polymerization, image smear is easy to be generated at high humidity. Details have not yet been clear, but a conventional PTFE possesses a high hydrophilic functional group such as a hydroxyl group or a carboxylic acid, reaction gas such as ozone or NOX generated during electrification at high humidity is easy to be picked up at the terminal of PTFE, and the generated acid is localized at the terminal of PTFE, whereby an ion conducting path is presumably easy to be formed.    (Patent Document 1) Japanese Patent O.P.I. Publication No. 2006-84941    (Patent Document 2) Japanese Patent O.P.I. Publication No. 2005-37562    (Patent Document 3) Japanese Patent O.P.I. Publication No. 2005-227742    (Patent Document 4) Japanese Patent O.P.I. Publication No. 6-236063    (Patent Document 5) Japanese Patent O.P.I. Publication No. 2006-184803